Secure supply reservoir for hydraulic circuit

ABSTRACT

A tank according to the invention comprises a casing, a filling port ( 5 ) extending, on the outside of said tank, into a filling neck ( 7 ), which is provided with a screw thread having a pitch (p) and which cooperates with a cap ( 9 ). The inner surface of the cap cooperating with the screw thread, at least one outlet port for the hydraulic-fluid flow towards a hydraulic circuit. Means ( 43 ) for the connection of the inner space ( 3 ) of the tank with the ambient air and comprising at least one transverse channel ( 45 ), more advantageously two channels ( 45 ), extending from a first lengthwise end ( 47 ) of the filling neck ( 7 ) to a second lengthwise end ( 49 ) of the filling neck ( 7 ), between the filling neck ( 7 ) and the cap ( 9 ) so as to connect the inside of the tank with the ambient air.

The present invention mainly relates to a hydraulic tank for animproved-safety supply of a hydraulic circuit with brake fluid and to abraking system fitted with such a tank and it relates, moreparticularly, to a brake-fluid tank for the supply of a braking circuitwith brake fluid and, more especially, for the supply of anelectrohydraulic braking circuit with brake fluid.

A braking circuit of a conventional type comprises a master cylinder,fed from a brake-fluid tank and actuated by an actuating rod, connectedwith a brake pedal, which is controlled by the driver. The brakingcircuits also comprise brakes, connected to the master cylinder and fromwhich they receive a pressure fluid on a braking action.

As regards the electrohydraulic braking circuits, in a normal operatingsituation, the braking is not taken charge of by the master cylinder butinstead by a pump, which delivers pressure fluid to the brakes mountedat the wheels of the vehicle. Such pump is controlled by a computer, onthe basis of braking information received from sensors, arranged e.g. atthe actuating rod. In an electrohydraulic braking circuit, and in anormal operating situation, the master cylinder is used for simulatingthe mechanical reaction of the braking circuit whereas, under deterioredconditions, for instance when either the computer or the hydraulic pumphappens to be unavailable, the master cylinder is used as the source ofpressure brake fluid for the brakes, quite conventionally.

In conventional braking circuits as well as in electrohydraulic brakingcircuits, the brake fluid is supplied from a tank. As concernsconventional braking systems, the tank is disposed on the mastercylinder and it delivers fluid to first and second hydraulic chambers,connected to the brakes while, in the case of electrohydraulic brakingcircuits, a first tank supplies the master cylinder with fluid and asecond tank feeds the hydraulic pump.

In the course of the gravity flow of the brake fluid from the tank tothe braking circuit, the brake-fluid volume contained in the tank isreducing, which means that a greater space is available for the airinside the tank, above the brake-fluid surface. It results in that theair pressure inside the tank is reducing too, and in that a negativepressure is created above the brake-fluid surface, which fact is likelyto stop or at least to impede the fluid flow into the master cylinder orits drawing by the hydraulic pump.

Accordingly, in a well-known manner, such tanks are fitted withbreathing means capable of supplying the inner space of the tank withatmospheric-pressure air, so as to equilibrate the inner pneumaticpressure of the tank with the ambient-air pressure in order to avoid anegative pressure.

In a well-known manner, such breathing means consist of a passageprovided at a filling neck for the supply of the tank with brake fluid.More especially, the neck, intended for the supply of the tank withbrake fluid, cooperates with a sealing means, for instance a cap,through a screw thread, the pitch of such screw thread cut in the capbeing such as to provide a passage connecting the inner space of thetank with the ambient air, thus letting air into the tank and avoidingthe detrimental influence of a negative pressure on the brake fluidinside the tank.

Yet, such air passage is small-sized in order to prevent a fluid flowout of the tank and an ingress of some foreign particulate matter intothe latter, which might interfere with a sound operation of the brakingsystem. Besides, the brake-fluid tank is arranged in the motorcompartment, which is not proof against outer pollutants and which issusceptible to a rapid fouling by foreign particles of any kindwhatsoever, e.g. dirt, grease, likely to block the passage, providedbetween the filling neck of the tank and the closing cap cooperatingwith such neck. When this air passage, connecting the outside with theinside of the tank is blocked, a negative pressure is created within thetank, which means that the brake-fluid flow towards the brakes can nolonger be steady, with the result that the braking efficiency willprobably be reduced.

Therefore, it is an object of the present invention to provide ahydraulic-fluid tank, for a reliable supply of a hydraulic circuit withhydraulic fluid.

Another object of the invention consists in providing a braking systemwith no risk of a loss in the brake-fluid supply.

These objects are achieved, in accordance with this invention, by ahydraulic-fluid tank, comprising a filling neck closed by a cap, meansfor the brake-fluid flow towards a hydraulic circuit and means for theconnection of the inner space of the tank with the outside and having anadequate cross-section area to preclude any blockage of said means,which are capable of cooperating with breathing means of a known type soas to improve their reliability.

In other words, these connecting means are transverse channels providedin the outer periphery of the filling neck and extending from the lowerpart of the neck to its upper part, and exhibiting a comparatively muchlarger cross-section area than that of the helical passage of thebreathing means of a known type.

The main subject of the present invention is a hydraulic-fluid tank,comprising a casing, defining an inner space, a filling port extending,on the outside of said tank, into a filling neck, which is provided witha screw thread having a given pitch and cooperating with a cap, theinner surface of said cap cooperating with said screw thread, at leastone outlet port for the hydraulic-fluid flow towards a hydrauliccircuit, means for the connection of the inner space of the tank withthe ambient air, characterised in that such means comprise at least onetransverse channel, more advantageously two channels, extending from afirst lengthwise end of the filling neck to a second lengthwise end ofthe filling neck, in the opposite direction to the first end, betweenthe filling neck and the cap so as to connect the inside of said tankwith the ambient air.

Another subject matter of the present invention is a tank, characterisedin that the transverse channels are radially opposite.

The present invention also deals with a tank, characterised in that thechannels are provided in the filling neck and intercept each thread ofthe screw thread of the filling neck.

Another subject matter still of the present invention is a hydraulictank, characterised in that, in an advantageous manner, the channels aresubstantially vertical.

According to another aspect of the invention, a hydraulic tank ischaracterised in that it comprises a helical passage connecting theinner space of the tank with the atmospheric-pressure air, and definedin part by the screw thread provided on the neck and by the innersurface of the cap.

Another subject matter of the present invention is a tank, characterisedin that a radially-outer end of the channels is formed by the inner wallof the cap grip.

Another subject matter still of the present invention is a tank,characterised in that, in an advantageous manner, the pitch p of thescrew thread ranges from 3 mm to 4 mm and is, more advantageously, equalto 3.67 mm.

This invention also deals with a braking system, comprising a mastercylinder, actuated by an actuating rod connected with a brake pedal, andcapable of delivering a pressure brake fluid to the brakes disposed atthe wheels of a vehicle, characterised in that it comprises a tank.

According to another aspect still of the invention, a braking system,which comprises a computer controlling a hydraulic pump for the supplyof the brakes with brake fluid in a normal operating situation, andwherein the master cylinder is used as a braking-feeling simulator in anormal operating situation, is characterised in that it comprises a tankfor the supply of the hydraulic pump with fluid.

Other features and advantages of the present invention will be apparentfrom the following detailed description, when taken in conjunction withthe accompanying drawings, in which:

FIG. 1 is a sectional side view of a preferred embodiment of a tankaccording to this invention

FIG. 2 is a view of a detail from FIG. 1;

FIG. 3 is a top view of a detail of the tank shown in FIG. 1; and

FIG. 4 is a diagram of an electrohydraulic braking system.

FIG. 1 shows a tank according to the present invention, which comprisesa casing 1 defining an inner space 3 containing a hydraulic fluid. Thetank also comprises a filling port 5 extending, on the outside of thetank, into a filling neck 7 with an axis X and closed by a cap 9, andthe tank also comprises outlet ports for the delivery of the hydraulicfluid to a hydraulic circuit.

The tank also comprises outlet ports 10: in a conventional brakingsystem, a first outlet port is intended for the supply of a primaryhydraulic circuit of a master cylinder, whereas a second outlet port isintended for the supply of a secondary hydraulic circuit of the mastercylinder.

As regards an electrohydraulic braking system, a first tank supplies themaster cylinder, such first tank being similar to that of a conventionalbraking system, while a second tank is provided with an outlet portconnected with a hydraulic pump, and a port for the reinjection of thebrake fluid after a brake-actuation phase.

The means, which are intended to fix the cap 9 in position relative tothe filling neck 7, consist of means for the screwing of the cap 9 onthe filling neck 7 and, more particularly, of the inner surface of agrip 11 forming the peripheral wall of the cap 9 on the outer surface ofthe filling neck 7.

FIG. 2 shows a detail view of the means intended to fix the cap 9 inposition on the filling neck 7, which also provide a breathing passagefor the inner space 3 of the tank.

Such breathing passage, which connects the inner space 3 with theambient air, is defined, on the one hand, by the inner wall of the grip11 of the cap 9 and, on the other hand, by the outer wall of the fillingneck 7.

The filling neck 7, having the axis X, comprises on its outer surface ascrew thread 26, the pitch of which ranges, in an advantageous manner,from 3 mm to 4 mm and is, more advantageously, equal to 3.67 mm, andwhich consists of an helix extending from a lower first lengthwise end47 of the neck 7 towards an upper second lengthwise end 49 of the neck7. The cross-section of the helix exhibits substantially the shape of aright-angled trapezoid, the major base of which is borne by the outersurface of the neck 7. The minor base of the trapezoid is parallel tothe major base, that is parallel to the axis X and it connects with theouter surface of the neck 7 through first and second sides, 31 and 33,that is a first inclined side 31 and a second side 33 which issubstantially perpendicular to the axis X.

The cap 9 comprises an internal thread, cooperating with the screwthread 26, cut in the outer surface of the filling neck 7. Said internalthread 32 is provided in the inner surface of the grip 11 and itconsists of a helical third inclined face 37 and of a helical fourthinclined face 39 exhibiting a cross section in the shape of asubstantially regular trapezoid, so as to define, on the fittingoperation, a gap between the second substantially-perpendicular side 33,borne by the neck 7, and the fourth inclined face 39 borne by the cap 9.

On the fitting of the cap 9 on the filling neck 7, the third inclinedface 37 comes into contact with the first inclined side 31 whereas ahelical gap 41 is formed between the fourth inclined face 39 and thesecond substantially-perpendicular side 33. In the ordinary course, thepassage 41, thus formed between the filling neck and the cap is enoughto ensure an air communication between the inner space 3 of the tank andthe ambient, so as to avoid a negative pressure inside the tank, whichwould impede the normal fluid flow into the braking circuit, likely tointerfere with a sound operation of the brakes.

Yet, it might happen that the helical passage 41 be blocked by someforeign particulate matter, e.g. dirt or grease, and that is the reasonwhy the tank according to the present invention comprises breathingmeans 43 consisting of at least one channel 45, which is substantiallycoaxial with the axis X of the filling neck, and which is provided inthe outer periphery of the neck, in the screw thread 26. The channel 45extends from the first lengthwise end 47 of the neck, facing the casing1, towards the second lengthwise end 49 of the filling neck, such secondend being open and letting the brake fluid in, thus intercepting thehelical passage 41 throughout its path.

Therefore, air circulates from the outside to the inner space of thetank, through the channel 45 provided between the outer surface of thefilling neck and the inner surface of the grip 11 of the cap. Mostadvantageously, this second breathing means comprises two channels 45,which are radially opposite and provided in the outer periphery of thefilling neck.

The cross-section area of the channels 45 is somewhat larger than thecross-section area of the helical passage 41, constituting the firstbreathing means. Therefore, the breathing means 43 are definitely lesslikely to be blocked by foreign particles. As a matter of fact, in spiteof their large size, these channels 45 preclude the ingress of foreignparticles into the inner space 3 of the tank, because their upper ends,communicating with the inside of the tank, are substantially closed bythe upper part of the cap, thus prohibiting the passing through of atleast the larger-size particles, which might interfere with a safeoperation of the braking circuit.

FIG. 4 illustrates a electrohydraulic braking system, comprising amaster cylinder 51, which is supplied with brake fluid by a first tank52 according to this invention, and which is connected to a brake pedal53 through an actuating rod 55. In a normal operating situation, themaster cylinder is used for simulating the mechanical reaction of thebraking circuit whereas, in a deteriorated operating state, it deliverspressure brake fluid to the brakes 57. The braking system also comprisesa computer 59 which commands a hydraulic pump 61, supplied with brakefluid from a second tank 62 according to the present invention, todeliver pressure brake fluid, on the detection of a necessary speedreduction for the vehicle.

Or course, the breathing means may comprise more than two channels, yettwo channels are quite capable of coping with a reliable breathing ofthe inner space of the tank.

It should be understood that the channels 45 may be provided so as to bedisposed at an nonzero angle to the vertical.

In the same way, the transverse channels 45 may be provided in the cap,in the inner surface of the grip 11 of the latter, bearing the internalthread 32.

The preferred embodiment of the tank according to the present inventioncomprises a breathing passage of a known type and breathing meansaccording to this invention, so as to improve the reliability of thebrake-fluid delivery to the braking circuit but, of course, thebreathing means according to this invention can be implementedindependently of the helical breathing passage.

The present invention applies to conventional braking circuits, fittedwith a master cylinder, which is actuated by an actuating rod in anormal braking situation.

Most advantageously, this invention applies to an electrohydraulicbraking system, wherein the normal braking action is taken charge of bya hydraulic pump, controlled by a computer so as to deliver a pressurebrake fluid to the brakes.

The present invention concerns, more particularly, the motor carindustry.

And the present invention mainly applies to the design and manufacturingof braking systems for motor vehicles and, more especially, of brakingsystems for private cars.

1. A Hydraulic-fluid tank, comprising a casing, defining an inner space(3), a filling port (5) extending, on the outside of said tank, into afilling neck (7), which is provided with a screw thread having a pitch(p) and which cooperates with a cap (9), the inner surface of said capcooperating with said screw thread (26), at least one outlet port forthe hydraulic-fluid flow towards a hydraulic circuit, means (43) for theconnection of the inner space (3) of the tank with the ambient air,characterised in that said means comprise at least one transversechannel (45), more advantageously two channels (45), extending from afirst lengthwise end (47) of the filling neck (7) to a second lengthwiseend (49) of the filling neck (7), in the opposite direction to the firstend (47) between the filling neck (7) and the cap (9), so as to connectthe inside of said tank with the ambient air.
 2. The Hydraulic-fluidtank according to claim 1, characterised in that the channels (45) areradially opposite.
 3. The Hydraulic-fluid tank according to claim 2,characterised in that the channels (45) are provided in the filling neck(7) and intercept each thread of the screw thread (26) of the fillingneck (7).
 4. The Hydraulic-fluid tank according to claim 1,characterised in that, in an advantageous manner, the channels (45) aresubstantially vertical.
 5. The Hydraulic-fluid tank according to claim1, characterised in that it comprises a helical passage connecting theinner space (3) of the tank with the atmospheric-pressure air, anddefined in part by the screw thread (26) provided on the filling neck(7) and by the inner surface of the cap (9).
 6. The Hydraulic-fluid tankaccording to claim 1, characterised in that a radially-outer end of thechannels (45) is formed by the inner wall of the grip (11) of the cap(9).
 7. The Hydraulic-fluid tank according to claim 1, characterised inthat, in an advantageous manner, the pitch (p) of the screw threadranges from 3 mm to 4 mm and is, more advantageously, equal to 3.67 mm.8. The Hydraulic-fluid tank according to claim 1 for use in a brakingsystem having a master cylinder, actuated by an actuating rod connectedwith a brake pedal, and capable of delivering pressure brake fluid tobrakes disposed at the wheels of a vehicle.
 9. The Hydraulic-fluid tankaccording to claim 8 for use in a braking system having a computercontrolling a hydraulic pump for the supply of the brakes with brakefluid in a normal operating situation, wherein the master cylinder isused as a braking-feeling simulator in a normal operating situation.